In the press extrusion process of metal, the material to be extruded such as billet, is loaded in a container and pushed by a stem provided with a head called a dummy block whose outer diameter is a little smaller than that of the inner diameter of the container in order to leave the surface layer of the billet intentionally in the container because that portion has usually been oxidized under heating or covered with hard scale which contamination may spoil the quality of the extruded product. The remnant shell necessitates cleaning operation per every extrusion stroke, e.g., with a stem fitted with a cleaning block on the front, that hampers the continuity of the extrusion operation cycle and thereby degrades the productivity of the extrusion operation.
An improved block or disc to overcome this shortcoming has already been invented, which comprises two disc portions, front and rear, to provide an annular recess portion therebetween for receiving the shell scraped and crushed during the successive extrusion stroke of the stem. However, the annular shell accumulates over the entire periphery of the recess portion of the disc and therefore the material solidified or the "shell" is quite difficult to release per se from the disc.
On the other hand, an attempt of using a sub-container for promoting the continuation of the extrusion process has been made. However, it also needs a removal of the extrusion remnant or butt of the billet by means of a shear or other means at each stroke of extrusion. Highly efficient removing of the remnant crust or shell sticking to the container bore and the disc thus can not be said to have been solved by these devices alone. They are still imperfect in respect to efficient removal of the remnant shell and the high cycle operation of the metal extrusion press, and are far from being continuous operation of the extrusion press.